1. Field of the Invention
The field of the present invention is generally directed to a solid-state switch. More specifically, the field of the present invention is directed to a solid-state switch for discharging an intermediate energy storage capacitor into a magnetic compression circuit for powering a laser, or for other applications requiring high current pulses.
2. Description of Related Art
Applications requiring very high current pulses of extremely short duration have steadily increased in number. One such application is a power supply for laser systems used in both industry and research. For the generation of high power pulses, voltages up to 20 kV generally must be switched in fractions of a microsecond.
Previously, this extremely short duration switching has been almost the exclusive domain of the electron tube or thyratron. Thyratrons, however, suffer from a number of disadvantages. Chief among these disadvantages is their limited effective lifespan. In applications to discharge a storage capacitor, such as into a magnetic compression circuit for high voltage applications, e.g. a laser, a thyratron experiences a characteristic operating life of some 1200 hours with a maximum lifespan of some 2500 hours.
A resultant second disadvantage of the thyratron therefore relates to its operating cost per unit-hour. The per unit cost of a conventional thyratron for high voltage applications is quite expensive and generally falls in the range of $6,000-$7,000 per unit. Once the thyratron fails which as noted above occurs often within a median operating life of some 1200 hours, the operating cost of a thyratron measured on a per hour basis averages approximately $5.50 per hour. This comparatively high per hour operating cost limits the applications for which the thyratron may be considered.
The use of thyristor switches for pulse generation is known. For example, Vitins, et al. Power Semiconductor Devices For Submicrosecond Laser Pulse Generation, ASEA Brown Boveri, Ltd. (1988); Vitins, et al. Reverse Conducting Thyristors Replace Thyratrons In Sub-microsecond Pulse Generation, BBC Brown Boveri, Ltd. (1987); Steiner, et al., Thyratrons In High-Current Pulse Applications, BBC Brown Boveri, AG (1988) and references cited therein disclose the use of thyristors with interdigitated, amplifying gate structures to provide very short high current pulses.
However, the conventional devices described in the foregoing references fail to address the problem of switch jitter. The elimination of jitter is crucial to ensure constant operation over a virtually unlimited number of current pulses for laser applications. The elimination of switch jitter is especially important as one increases the generation of high power pulses. If firing jitter is not controlled, circuit performance is degraded particularly when using magnetic compression techniques.
In addition, conventional RCT devices require overvoltage protection to protect the RCTs, particularly when RCTs are configured in a series stack. The importance of limiting jitter and providing overvoltage protection to prevent the literal burnout of the SCR portion of a conventional RCT device at extremely high frequencies may be explained as follows. Conventional devices which use RCTs to produce submicrosecond pulses discharge a high voltage capacitor to drive a load such as a laser. In conventional devices, RCTs are linked together in series and are triggered simultaneously. A high voltage capacitor then discharges through a magnetic assist and through all the RCTs in series and into the load. Prior art has not been demonstrated at more than four RCTs in series, nor has the problem of switch jitter been addressed.
One aspect of the present invention incorporates overvoltage protection through the use of break-over diodes (BODs). Known prior art devices have identified the use of BODs for this application. However, the present invention solves the problem of a subtle noise induced failure mechanism of the BOD due to stray capacitance, which is not addressed by the prior art. It has been found that when using a relatively large number of RCTs in series, the stray capacitance associated with each RCT can result in false triggering effects caused by BOD failure.